Transcript Chapter 5 - EZWebSite

Chapter 5
Periodic Law
Section 5-1
History of the Periodic Table
The 1800’s – A Time of
Chemical Discovery
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In the 1800’s, new elements were being
discovered at a fast rate.
Scientists realized they needed a way to
classify them.
Also needed a method to determine atomic
mass.
In 1860, a conference determined how to find
relative atomic mass.
Dmitri Mendeleev (1834 –
1907)
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Used new atomic
mass values in a
textbook.
Attempted to
organize elements
according to their
properties.
Mendeleev discovered periodic
trends
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When he arranged elements in order of
increasing atomic mass, similarities in
properties appeared at regular intervals.
This pattern is referred to as periodic.
The First Periodic Table
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Mendeleev grouped
elements with
similar properties
together, to create
the first periodic
table.
A copy is found on
page 124.
Unique Characteristics of
Mendeleev’s Table
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Mendeleev left gaps in
his periodic table.
These can be seen at
elements 45,68, 70.
Mendeleev predicted
both existence and
properties of these
elements.
Filling the Gaps
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By 1886, all three of
these elements were
discovered.
These are now known
as Sc, Ga, and Ge.
The properties of these
three are very similar to
what Mendeleev
predicted.
Mendeleev’s Periodic Table
Worked.
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As a result of his
successful
predictions, the
scientific community
was forced to take
Mendeleev seriously.
Mendeleev’s Periodic Table
Worked
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Mendeleev became
known as the
founder of periodic
law.
Criticisms of Mendeleev’s
Table
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Mendeleev did not exactly follow the order of
atomic mass.
Notice that Te, with an atomic mass of 128
comes before I with an atomic mass of 127.
The scientific community disregarded
Mendeleev’s work because he changed his
rules to fit his table.
Henry Moseley – (1887 –
1915)
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Studied atomic emission
spectra.
Found a pattern in
them.
Led him to discover
atomic number.
Mendeleev’s periodic
table was in perfect
order of atomic number.
Periodic Law
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Moseley’s discovery changed the
definition of periodic law.
The periodic law states that when
elements are arranged in order of
increasing atomic number, elements
with similar properties will appear at
regular intervals.
The Modern Periodic Table
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Over 40 new elements have been
discovered since Mendeleev.
Most of these can be grouped by
properties with other elements, but
some form three new groups.
Three New Groups of
Elements
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Noble Gases – Group
VIII A. These are
difficult to observe
because they are
odorless, colorless, and
very unreactive.
Lanthanides – the 14
elements from 58 to 71.
Actinides – the 14
elements from 90 to
103.
Periodicity
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All group A elements show periodicity.
The pattern of periodicity in group A elements
is: 8, 8, 18, 18, 32. These are the numbers
of elements between elements with similar
properties.
The periodic table is divided into four
sections.
Section 5-2
Electron Configuration and the
Periodic Table
The s - block
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S – block elements are chemically reactive metals.
All group 1 elements end in s1.
Group IA elements are called alkali metals.
They are more reactive than Group IIA.
All have a silvery appearance and can be cut with a
knife.
All react strongly with water, and can pull moisture
out of the air.
Are usually stored in oil, and are rarely found in a
pure form in nature.
The s - block
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Group IIA elements are called alkaline earth
metals.
All of their electron configurations end in s2.
Harder, denser, and stronger than alkali
metals.
Higher melting points, and are less reactive,
but still too reactive to be found in nature.
The s - block
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Helium and Hydrogen are special cases.
Hydrogen ends in s1, but is not an alkali
metal. It is a unique element that is
considered to be in its own family, and
its properties do not resemble those of
any known group.
The s - block
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Helium ends in s2.
However, it is more closely related to
elements in group VIIIA.
Since the first energy level has only an s
orbital, and two electrons fill it, helium has a
full outer energy level.
This gives it the same stability and
unreactivity as a noble gas.
The d - block
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More complex electron configurations.
All metals, called transition metals.
They are lustrous, and good conductors.
These are more typical metals.
Palladium, Platinum, and Gold are among the
least reactive elements.
All transition metals are less reactive than the
s – block.
The p – block, Groups IIIA VIIIA
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Contains mostly nonmetals, a few metals,
and all metalloids.
Group VIIA are the halogens, which are the
most reactive nonmetals. They all form salts
with metals. F and Cl are gases, Br is the
only liquid nonmetal, and I is a solid. As is
synthetic.
The p – block, Groups IIIA VIIIA
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The metalloids are found along the stair step
line, and are all brittle solids. They are also
good semiconductors.
The metals in the p – block are harder and
denser than s – block metals, but softer than
transition metals. They are also stable in air.
The f – block elements, the
Lanthanides and the Actinides
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Found at the bottom of the
periodic table. These are
called Rare Earth Metals.
Lanthanides are shiny and
relatively reactive, like group
IIA.
Actinides are all radioactive.
The first four are found on
earth, all others are man –
made.
Arrangement of the Periodic
Table
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The periodic table is arranged so that the
period number is equal to the highest
occupied energy level.
The length of a period also equals the
number of electrons in an energy level.
The number of electrons in the highest
energy level for all group A elements is equal
to the group number.
Section 5-3
Electron Configuration and
Periodic Properties
Atomic Radius
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One half the distance between the
nuclei of two identical atoms that are
bonded together.
What happens to Atomic Radius as you
travel from left to right across a period?
Atomic Radius
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It decreases.
As you move across the period you add more
electrons to the same energy level, but you
also add more protons to the nucleus. More
protons exerts a stronger attractive force and
pulls the electrons in more tightly.
What happens to atomic radius as you go
down a group?
Atomic Radius
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It goes up.
While you add more protons to the nucleus,
which exert a stronger pull, you also add
more electrons, but this time, you add them
in higher energy levels. These higher energy
levels are farther from the nucleus, making
the radius larger.
Fr has the largest radius, He the smallest.
Ionization Energy
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The energy required to remove an
electron from a neutral atom.
An ion is an atom or group of atoms
with a positive or negative charge.
As we move from left to right across a
period, does ionization energy go up or
down?
Ionization Energy
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It goes up.
Electrons are held more tightly by the
nucleus, and so, are harder to remove.
Generally, you can only remove
electrons from Groups IA, IIA, and IIIA.
In some cases, they can also be
removed from IVA.
Ionization Energy
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Some elements, particularly those in groups
IIA and IIIA, can lose more than one
electron. The energy required to do this is
called the second or third ionization energy.
These are always higher than the first
ionization energy. This is because as each
electron is removed, the others are held more
tightly by the nucleus.
Ionization Energy
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As a rule, Group IA loses one electron, Group
IIA loses two electrons, and Group IIIA loses
three electrons. The transition metals also
lose electrons, but the number varies due to
the overlap of orbitals.
What happens to Ionization Energy as you go
down a group?
Ionization Energy
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It goes down.
As you go down a column, you add
energy levels to each atom. The
energy levels put the outer electrons
farther away from the nucleus.
Electrons that are farther from the
nucleus are easier to remove.
Electron Affinity
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The energy change that occurs when a
neutral atom gains an electron.
Most atoms release energy as they gain
electrons.
As you move from left to right on the
periodic table, what happens to electron
affinity?
Electron Affinity
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It goes up.
In most cases, only the elements in Group
VA, VIA, and VIIA gain electrons, and so they
have the highest electron affinity. This is
because they have more protons in their
nuclei, and so attract electrons more strongly.
Electron Affinity
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Some atoms can gain more than one electron.
Generally, atoms in Group VA gain three electrons,
atoms in group VIA gain two electrons, and atoms in
group VIIA gain one electron.
The second or third electron affinities are usually
lower than the first. This is because you have the
same number of protons pulling on more electrons so
they pull more weakly.
Electron Affinity
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Group VIIIA, the noble gases, have no
electron affinity. They have a full
sublevel, and do not need them.
The same is true of group IIA.
The d-block and f-block have
unpredictable electron affinities.
Electron Affinity
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What happens to electron affinity as
you move down a group?
It goes down.
The larger size of the atoms keeps the
electrons farther from the nucleus, and
therefore they are not attracted as
strongly.
Ionic Radius
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Ionic Radius is determined by the type
of ion formed.
A positive ion is a cation. These tend to
be smaller than the atom they came
from. These are formed by Group IA,
IIA, and IIIA, and the transition metals.
Ionic Radius
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A negative ion is an anion, and they tend to
be larger than the atom they came from.
These are formed by Group VA, VIA, and
VIIA.
Ionic Radius tends to decrease from left to
right across a period. It tends to increase
going down a column.
Ionic Radius
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As a rule, metals tend to form cations,
and nonmetals form anions.
Group IVA and VIIIA do not gain or lose
electrons, and so, do not form ions.
Electronegativity
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A measure of the ability of an atom in a
compound to attract electrons.
Tend to increase going from left to right
across a period, and decrease going down a
column.
Noble gases have no electronegativity, since
they do not form compounds.
Electronegativity
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The most
electronegative
element is F,
fluorine.
The least
electronegative
element is Fr,
francium.
Valence Electrons
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Any electron in the highest occupied energy
level.
Eight valence electrons provides the
maximum stability an atom can have. This is
referred to as the octet rule.
The number of valence electrons in each
group A element is equal to its group number.